Protein kinases are a family of enzymes that catalyze phosphorylation of the hydroxyl groups of specific tyrosine, serine, or threonine residues in proteins. Typically, such phosphorylation can dramatically change the function of the protein and thus protein kinases can be pivotal in the regulation of a wide variety of cellular process, including metabolism, cell proliferation, cell differentiation, and cell survival. The mechanism of these cellular processes provides a basis for targeting protein kinases to treat disease conditions resulting from or involving disorder of these cellular processes. Examples of such diseases include, but are not limited to, cancer and diabetes.
Protein kinases can be broken into two types, protein tyrosine kinases (PTKs) and serine-threonine kinases (STKs). Both PTKs and STKs can be receptor protein kinases or non-receptor protein kinases. PAK is a family of non-receptor STKs. The p21-activated protein kinase (PAK) family of serine/threonine protein kinases plays important roles in cytoskeletal organization and cellular morphogenesis (Daniels et al., Trends Biochem. Sci. 24: 350-355 (1999); Sells et al., Trends Cell. Biol. 7: 162-167 (1997)). PAK proteins were initially identified by their interaction with the active small GTPases, Cdc42, and Rac, and their homology to yeast kinase Step 20 (Manser et al., Nature 367: 40-46 (1994)). In addition to mediating the regulation of actin cytoskeleton and cell adhesion by Cdc42 and Rac (Daniels et al., Trends Biochem. Sci. 24: 350-355 (1999)), it was determined that some PAK proteins protect cells from apoptosis (Gnesutta et al., J. Biol. Chem. 276: 14414-14419 (2001); Rudel et al., Science 276: 1571-1574 (1997); Schurmann et al., Mol. Cell. Biol. 20: 453-461 (2000)); modulate mitogen activated protein (MAP) kinase pathways (Bagrodia et al., J. Biol. Chem. 270: 27995-27998 (1995); Brown et al., Curr. Biol. 6: 598-605 (1996); Chaudhary et al., Curr. Biol. 10: 551-554 (2000); Frost et al., EMBO J. 16: 6426-6438 (1997); King et al., Nature 396: 180-183 (1998); Sun et al., Curr. Biol. 10: 281-284 (2000)); mediate T-cell antigen receptor (TCR) signaling (Yablonski et al., EMBO J. 17: 5647-5657 (1998)); and respond to DNA damage (Roig et al., J. Biol. Chem. 274: 31119-31122 (1999)). Through these diverse functions, PAK proteins regulate cell proliferation and migration.
The full-length PAK4 nucleic acid and amino acid sequences are disclosed in U.S. Pat. No. 6,013,500 and have been deposited in GenBank under accession numbers AF005046 (mRNA) and AAD01210 (amino acid). Modulation of human PAK4 activity is reported to result in alterations in cellular processes affecting cell growth and adhesion. For example, overexpression of PAK4 in fibroblasts leads to morphological changes that are characteristic of oncogenic transformation through induction of anchorage-independent growth and inhibition of apoptosis (Gnesutta et al., J. Biol. Chem. 276:14414-14419 (2001); Qu et al., Mol. Cell. Biol. 21: 3523-2533 (2001)). More recently, it was also shown that: PAK4 is frequently overexpressed in human tumor cell lines of various tissue origins; expression of an active PAK4 mutant has transforming potential, leading to anchorage-independent growth of NIH3T3 cell line; and a kinase-inactive PAK4 efficiently blocks transformation by activated Ras and inhibits anchorage-independent growth of HCT116 colon cancer cells. These data strongly implicate PAK4 in oncogenic transformation and suggest that PAK4 activation is required for Ras-driven, anchorage-independent growth of human cancer cells. (Smeal, et al, J. Biol. Chem. 277, 550-558 (2002)) In vivo efficacy in mice with implanted tumor of a compound that inhibits the PAK4 kinase domain is shown in the current application.
PAK4 therefore appears to us to be an attractive target for developing therapeutic agents effective for treating disorders involving abnormal cell growth, especially cancer.
For other background references, see U.S. Patent Application Publication No. 2003/0171357 and PCT Publication WO02/12242.